This invention relates to the stabilization of microbicides. In particular, this invention relates to the improved stabilization of 3-isothiazolone concentrate compositions.
Microbicides are used commercially to prevent the growth of microbes in a variety of loci, such as cooling towers, metal working fluid systems, paint and cosmetics. One of the more important classes of microbicides is 3-isothiazolones. Many 3-isothiazolones have achieved commercial success because they are very effective in preventing microbial growth under a wide variety of conditions and in a variety of loci. Among the most important 3-isothiazolones are 5-chloro-2-methyl-3-isothiazolone, 2-methyl-3-isothiazolone, and mixtures thereof.
While 3-isothiazolones are very effective microbicides, they suffer from being unstable under certain conditions. Without the presence of a stabilizer, many 3-isothiazolones chemically degrade and lose microbicidal efficacy. Much research has been devoted to stabilizing 3-isothiazolones.
In general, compounds that stabilize 3-isothiazolone concentrates do not stabilize 3-isothiazolone dilute solutions. Compounds, such as magnesium nitrate, that do stabilize both 3-isothiazolone concentrates and dilute solutions do so in greatly differing amounts. More magnesium nitrate is required to stabilize a 3-isothiazolone dilute solution than a concentrate; 23 percent by weight for dilute solutions as compared to 12 to 16 percent by weight for concentrates. As dilute solutions are typically prepared by diluting 3-isothiazolone concentrate compositions, this need for additional stabilizer results in increased cost and handling.
Typical 3-isothiazolone products of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone contain between 1 and 25 percent by weight of the 3-isothiazolone mixture and a similar amount of a stabilizer. Concentrate compositions of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone generally contain about 5 to 35 percent by weight of the 3-isothiazolone compounds and require about 10 to 25 percent by weight of a stabilizer, such as magnesium nitrate. Dilute solutions of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone contain about 0.5 to 5 percent by weight of the 3-isothiazolone compounds.
A variety of stabilizers for 3-isothiazolone concentrates are known. These known stabilized 3-isothiazolone dilute solutions suffer from having a high metal salt content or from having limited stability. When a 3-isothiazolone stabilized with a metal salt is added to a latex formulation, the high metal salt content can coagulate the latex. U.S. Pat. No. 5,145,501 (Lashen, et al.), herein incorporated by reference, discloses the stabilization of 3-isothiazolone concentrates with a metal bromate salt. The problem with these compositions is that any non-halogenated isothiazolones become brominated upon storage, resulting in limited stability of the 3-isothiazolones. This patent also teaches that chlorate and perchlorate salts do not stabilize 3-isothiazolones. Moreover, this patent does not address the problem of precipitate formation upon storage of the 3-isothiazolone compositions.
Although the use of stabilizers enables 3-isothiazolone products to retain their microbicidal efficacy for considerable periods of time, other problems may develop without significant loss of 3-isothiazolones, such as the formation of precipitate upon storage. The presence of this precipitate does not impact the efficacy of the 3-isothiazolones; however, the presence of the precipitate gives an undesirable appearance to users of the product. It is clearly preferable from a commercial standpoint to have a product which does not form a precipitate.
Thus, there is a continuing need for stable 3-isothiazolone concentrate compositions that remain stable when diluted to form dilute solutions without the need for additional stabilizer and are free of precipitate.